Oman’s Hajar Mountains hosts a large slab of oceanic crust composed of serpentinized ultramafic rocks, the largest exposure of such rocks on Earth’s surface. These distinctive rocks contain fossil evidence of microbes that once lived in the subterranean environment where these rocks form.
A team of Arizona State University scientists led by Jon Lima-Zaloumis, an ASU graduate student and current postdoctoral fellow at the School of Earth and Space Exploration, participated in the Oman Drilling Project (OmanDP) and was able to examine drill core samples of the Samail ophiolite. By examining these samples in detail using instruments available at ASU and abroad, the team was able to uncover fossil evidence of microbes that once lived and were subsequently buried in the underground serpentine environment.
For Lima-Zaloumis, this work is notable because there are relatively few publications examining whether microbes can be preserved in environments where serpentine rocks form.
“Researchers are interested in these systems from an astrobiological perspective because microbes can thrive on the water-rock reactions associated with serpentinization,” Lima-Zaloumis said. “Although we know that these systems can host active microbial ecosystems, it was previously unclear whether these systems can also lead to fossilization.”
This is significant as it highlights a unique geological setting in which to uncover ancient evidence of life on Earth and possibly beyond. The results of their findings were recently published in Nature Communications Earth & Environment with lead author Lima-Zaloumis and co-author Maitrayee Bose, an assistant professor at ASU’s School of Earth and Space Exploration.
“Our work may be useful for current and future planetary exploration missions with astrobiology-oriented targets and underscores the importance of serpentine rocks as targets for future exploration,” said Lima-Zaloumis. “For example, serpentine has been detected from orbit inside and around Jezero Crater, the site of the current Perseverance rover on Mars. When the rover encounters such rocks, our work underscores that they could be prime targets in the search for evidence of past life.”
Lima-Zaloumis and his team spent several months looking for signs of life in these samples, which required many hours of microscopy and scanning electron microscopy. They hypothesized that if signs of life were found, it would occur in mineral-filled fractures that were common in the upper sections of drill core (visible in the images above).
The team had an “aha” moment when they finally found clusters of potentially biological-looking structures trapped by calcium carbonate minerals. Much time was spent examining the morphology and chemistry of these structures to convince them that they were probable microbial remnants.
Serpentine environments have attracted a lot of attention as they are places where microbes can thrive through water-rock reactions, and scientists think these processes may be ubiquitous beyond Earth. Hydrogen released during serpentinization can be a source of chemical energy in the subsurface of Mars and in the frigid ocean worlds like Europa and Enceladus in the outer Solar System.
Lima-Zaloumis and the team hope their research will draw more attention to serpentine environments as locations where fossil evidence of microbes can be found.
“Redox gradients in serpentine systems are capable of generating amino acids and other organic materials associated with life, making this work extremely relevant for missions to Mars and marine worlds,” Bose said.
Lima-Zaloumis said he’s hopeful that future studies will uncover more examples of fossilized organisms in serpentines around the world, which will help researchers develop a fuller understanding of how ubiquitous (or not) these conservation processes are and how these teachings can best be applied to similar rocks beyond the earth.
Other authors involved in this study are Anna Neubeck, Uppsala University, Department of Palaeobiology Geocentrum, Villavägen; Magnus Ivarsson, Swedish Museum of Natural History, Department of Paleobiology; Rebecca Greenberger, Caltech Division of Geology and Planetary Sciences; Alexis S. Templeton, University of Colorado, Department of Geological Sciences; Andrew D. Czaja, University of Cincinnati, Department of Geology; Peter B. Kelemen, Columbia University, Lamont-Doherty Earth Observatory; and Tomas Edvinsson, Uppsala University, Department of Materials Science and Engineering.
Preservation of microbial biosignature in carbonated serpentine from Samail Ophiolite, Oman, Communications Earth and Environment
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